The invention relates to a flaring tool for hollow, especially hollow cylindrical, workpieces, having a tool body with a bore, a flaring punch mounted for axial displacement therein whose outer tapered end protrudes from the bore, a cam likewise journaled in the tool body on a fulcrum axis perpendicular to the bore axis and operated by a hand lever by which the flaring punch can be displaced by a given amount away from the tool body out of a set of flaring dies that are joined to the tool body.
A flaring tool of this kind is disclosed in U.S. Pat. No. 4,034,591. The flaring punch mounted for displacement in the base tool body can be moved in only one direction by operating the lever, namely in the direction producing a radial outward displacement of the flaring dies. When the hand lever is moved in the opposite direction, the cam lifts away from the flaring punch. Nor can the annular spring associated with the flaring dies push the punch back, since the punch is provided with a very slender tapered end on account of the desire for a low actuating force on the hand lever, so that the system operates close to the taper-locking point. In order therefore to be able to remove the flaring dies from the flared workpiece, the dies must be first loosened by shaking the tool or tapping it. While in the case of metal workpieces, such as copper pipe for example, this method is successful because, after flaring, the material can no longer contract again. Such loosening is impossible in the case of materials which have a tendency to return to their original shape by "creeping." This characteristic is present, for example, in numerous high-strength plastics, such as are used today in plumbing, but especially for so-called "hydronic floor heating." These pipes have a marked shape-recovering ability and recover their shape in very little time, so that in any case it is not easily possible, when using the known flaring tools, to remove the flaring dies from the workpiece in time. Pipes made from plastic tend to shrink onto the flaring dies to a certain extent.
Although a spring to return the flaring punch is described in U.S. Pat. No. 4,034,591, its disposition is limited to a so-called adapter, as provided as a transitional piece in conjunction with relatively large sets of flaring dies. But even a return spring of this kind would not be suitable for solving the problem if it were contained in the tool body. For in the flaring of plastic pipes, the strength of the return spring is not sufficient to bring the punch back to the required end position. On the one hand the action of the spring is limited only to part of the travel of the flaring punch, and on the other hand the spring cannot be made arbitrarily strong since the return force must, of course, be overcome in addition to the flaring force when the tool is operated. Here, too, experience has shown that plastic pipes seize tightly on the flaring dies after the flaring operation, on account of their rapid shrinkage.
It is furthermore known to provide flaring punches for such tools with a positive return by driving them with a threaded spindle. As a rule the threaded spindle is driven by a so-called ratchet. A threaded spindle, however, can perform the reverse movement of the punch only very slowly. If a ratchet is used, its driving direction must also be reversed, or the ratchet must be reversed, so that considerable time passes before the flaring punch has begun, much less completed, its return movement. The result is, again, a seizure of plastic tubes onto the flaring dies.
The known flaring tools have therefore been limited, as a rule to use on metal workpieces. However, as is explained below, there is also a need for a flaring tool which is capable of flaring plastic pipes.
When plastic pipes are used in plumbing, especially in the production of hydronic floor heating systems, sections of finite length of such pipes have to be joined together. This is accomplished with so-called double-ended nipples which are shaped at both ends a serrated profile, as is the known practice in the case of garden hose couplings. Since the inside diameter of these nipples must not be substantially less than the inside diameter of the plastic pipes to be joined, and the nipples must still have sufficient thickness even between the serrations, the ends of the plastic pipes must be correspondingly flared to a depth that corresponds to approximately half the length of the nipple. In making such connections, use is already made of the property of such plastic pipes of shrinking very quickly onto the nipples in an absolutely leak-proof and mechanically strong manner. This shrinking characteristic of the plastic, that is so desirable in producing the bond between the nipple and plastic pipe, is extremely disadvantageous, however, in the case of the flaring operation itself, in that the operator is obliged to work very rapidly and, after flaring the pipe end, must not only remove the flaring tool from the end of the pipe but also insert the one end of the nipple, whose other end, in half of all the cases, is already joined to a long piece of pipe.
On account of the above-described behavior of the materials in question it is also impossible, for example, to prepare a large stock of flared plastic pipes, as would be easily possible in the case of metal pipes, which afterward can be joined together in a water-tight manner only by soldering.
It is therefore the object of the invention to improve a flaring tool of the type described above so that its flaring punch can be extracted from the end of the workpiece within the shortest possible time.